Actually, cultural preferences can change. This blog entry commenting on the NYTimes article mentions that both Japan and Korea have in recent decades begun to prefer daughters:
I've heard that this had lead to an increase in human trafficking, namely women in poorer countries like North Korea being "imported" and taken as brides.
On the former, investing in a chain of gay friendly bars or websites in China might be a good idea. It looks like the laws are getting a bit more lax in that area[1].
However, given the thousands-years cultural norm that prefer boys over girls, it's likely the gap will likely persist for a long time to come.
Anyone has some ideas on what to do with this problem?